1. Field of the Invention
The present invention relates to guiding and restoring heat losse to a hot metallic workpiece during advancing movement by a conveyor and, more particularly, to a method and apparatus for providing a carrier to support burners for movement between operable and service positions of which in the operable position the burners direct hot products of combustion from utility pockets through window openings in a side guide toward piece to restore heat to the metallic workpiece and in the service position the carrier including the burners and utility lines therefore are moved to a service position remote to the side guide to allow servicing of the burners and after servicing the burners supported by the carrier are returned to the operable position without disruption to the operation of the side guide and other burners spaced horizontally thereto.
2. Description of the Prior Art
While not so limited, the present invention is particularly useful to offset heat losses in a semi-finished hot mill workpiece before processing in a finishing mill train of a hot mill. Such a hot mill for the purpose of practicing the present invention includes continuous and semi-continuous hot strip mills and hot plate rolling mill. The hot metal workpiece treated according to the method and apparatus of the present invention includes but not limited to steel, aluminum, brass, titanium and beryllium. In a conventional continuous hot strip mill, an example of which is illustrated in FIG. 1A, steel slabs are introduced by pushers P into reheat furnaces F where a succession of slabs are heated to a highly heated state for hot metal working operations. When each slab attains a desired temperature for hot working, the slab is extracted from the furnace and conveyed by a furnace discharge table FDT to a vertical edging mill E, thence to a horizontal edging breaker B and thence to a tandem arrangement of roughing mill stands RMS. The edging mill E imparts a uniform width to the hot slab along the length thereof and the scale breaker B loosens and clears scale from the surface of the slab before the slab is reduced in thickness in the roughing mill stands RMS. The thickness of the slab after hot rolling and emerging from the roughing mill stands is of the order of 1 to 2 inches. After rolling in the roughing mill stands, the hot metal workpiece resides on a holding table HT. The holding table and the tables between the roughing mill stands and the furnace delivery table all incorporate spaced apart table rollers driven by motors to advance the workpiece along the roller tables of the hot mill. Side guides are arranged along the opposite sides of the holding table to center and direct the hot metal workpiece into a crop shear CS which imparts a squaring cut to the leading end of the workpiece before entry into the first mill stand of a tandem arrangement of finishing rolling mill stands FS. The thin hot strip workpiece emerging from the finishing mill stands has a thickness which is determined according to a preset rolling schedule. Coolant water is discharged onto the strip on run out table ROT as the strip is delivered to coilers C. A coil delivery conveyor CDC delivers the coils of hot strip from the coilers of the rolling mill installation for further processing. The holding table HT forms a delay site where the hot metal workpiece resides until an preceding hot metal workpiece is completely discharged from the run out table ROT and coiled by coilers C.
As typically illustrated in FIG. 1B, the hot workpiece residing on the holding table may have a length of 150 to 300 feet or greater and throughout after discharge from the furnace up to and including the delay period on the holding table, the hot metal workpiece undergoes atmosphere cooling. Not only is the hot workpiece residing on the delay table relatively long in relation to thickness, but it is usually at least 2 feet and up to six or more feet wide. Because of the hot metal workpiece takes the form of a relatively thin ribbon shaped workpiece and the transverse cross-sectional configuration is rectangular, unwanted atmospheric cooling is particularly acute at the workpiece edge corners WEC as compared to the central body area CBA of the hot workpiece. The relatively cooler outer edge corners WEC of the workpiece, impede plastic metal flow usually achieved during hot working operations and cause cracks that commonly develop as the workpiece undergoes one or a series of reduction to the thickness to attain the final desired gage in the finishing mill stands FS. The hot strip mill product with the edge cracks that commonly develop under these circumstances must be processed through an edge trimmer or similar process to restore structural integrity to the strip along its entire length. The resulting losses of the strip material due to the trimming operation are representative of significant loss to the economy of the hot strip mill installation, not only because of the metal loss from each coil, but the additional cost for processing represented by the required side trimming operation.
Attempts to maintain a constant temperature across the width of the hot workpiece have not met with success. A tunnel shaped furnace arranged to enclose the length of the hot metal workpiece at the entry side of the rolling mill stands requires an excessive amount of space, restricts access to the area and represents a substantial capital investment. The provision of such a tunnel shaped furnace is impractical particularly as a retrofit furnace to an existing rolling mill installation. Electrical induction heating of the longitudinal side edges of the hot workpiece was successfully demonstrated. However, precise alignment was required between a cavity of a "C" shaped heating die and the edge of a hot metal workpiece. Moreover, the heating dye was exposed to damage by impact upon initial advancing movement by the hot metal workpiece. This is because the leading edge of the workpiece was sometimes bent and distorted and thus precise alignment could not be readily achieved with the dye. As a result, such electrical heating is not practical. As an alternative to electrical heating, acetylene fuel gas heating of the workpiece edge is also effective. Because of the nature of the flame, the Acetylene fueled burners were located at such a close proximity to the edge of the workpiece that the burners were highly susceptible to damage because of mechanical shock, impact and air born debris from the hot metal workpiece. The burners were found to be a high maintenance item and not suitable for operation in hostile operating environment of a hot mill. Acetylene, as a fuel gas, increased significantly the operating cost and combustion of a gas produced intense localized heating imposing demands for critically precise control to avoid workpiece overheating and damage. Moreover, burner maintenance contributed materially to the downtime particularly because access to the burner was precarious and servicing of the burners necessitated the shut down of the hot mill facility and thus loss of production for an extended period of time. Also, the burners were not protectively housed against damage due to impact with the hot metallic workpiece during heating thereof.
Burners designed to heat side edges of a workpiece by producing combustion products using natural gas and oxygen have been tried but were also found to be a high maintenance item and not suitable for operation in hostile operating environment of a hot mill. The burners were secured directly to guides for the hot workpiece. The mounting arrangement was such that access to the burners and the required utilities was restricted and required an inordinate amount of service and maintenance particularly to perform cleaning operations as well as replacement of worn and damaged parts. The burners fueled by natural gas also were not protectively housed against damage due to impact with a hot metallic workpiece during heating thereof.
It is an object of the present invention to provide an improved guide design to guide hot metallic workpieces and provide discrete sites for operating and maintenance of burners used to heat opposed side edges of the hot metallic workpieces for subsequent hot metal processing.
It is a further object of the present invention to provide an improved guide design for hot metallic workpieces incorporating utility pockets communicating with window openings to allow an arrangement of burners in the utility pockets to discharge products of combustion toward opposite edges of the workpiece for heating thereof and positioning of the burners including utility ducts therefore as a unit in an inoperative position for servicing without disrupting the required operation of the guides used for positioning hot metallic workpieces for subsequent hot metal processing.
It is still another object of the present invention to provide a method and apparatus to offset heat losses at corner edges of hot metallic workpieces and eliminate or at least reduce side trimming losses of the subsequently finished metal product heretofore required to eliminate cracked marginal edges.